The present invention relates to reductive amination processes useful in the selective production of aminoethylethanolamine (AEEA). More specifically, the invention provides catalysts, which when used with specific promoters in the reductive amination of monoethanolamine (MEA) and ammonia, produce a product composition having higher levels of aminoethylethanolamine and reduced levels of cyclics such as piperazine (PIP).
AEEA is typically considered a by-product of processes used in the preparation of ethylenediamine (EDA). A significant portion of EDA made commercially is by the continuous reaction of monoethanolamine (MEA) and ammonia in the presence of hydrogen over a fixed bed reductive amination catalyst. The reaction generates a variety of polyalkylene polyamines as well. Illustrative of many of them are the following:
AEEA-N-(2-aminoethyl)ethanolamine PA1 PIP-Piperazine PA1 HEP-N-(2-hydroxyethyl)piperazine PA1 AEP-N-(2-aminoethyl)piperazine PA1 DETA-Diethylenetriamine PA1 TETA-Triethylenetetramine PA1 TEPA-Tetraethylenepentamine PA1 PEHA-Pentaethylenehexamine
Until recently, AEEA was viewed as an unwanted by-product and a precursor to PIP (see U.S. Pat. Nos. 2,479,657 and 3,383,417). The value of AEEA has risen considerably in recent years because significant commercial uses have evolved for it. Because most commercial processes have been designed to produce EDA and minimize the formation of PIP, owing to the limited demand for PIP, little is known about the manipulation of the commercial reductive amination processes to generate larger amounts of AEEA. There are very few patents directed to the manufacture of AEEA, and most do not rely on the reaction of MEA and ammonia under reductive amination conditions.
The following patents are directed to reductive amination processes for producing alkyleneamines product mixtures, which may contain AEEA in the product mix.
U.S. Pat. No. 4,123,462 describes a nickel-rhenium reductive amination catalyst for the production of desirable alkylamines and reduction of undesirable by-products having improved selectivity and increased conversion. The nickel-rhenium catalyst comprises rhenium and nickel impregnated on a support material selected from the group consisting of aluminas, silicas, silica-aluminas, kieselguhrs or diatomaceous earths and silica-titanias. The patent suggests that when selectivity is of primary concern, the amination process should not be run at high conversions, as it has been found that selectivity to the preferred aminoalkanes decreases as conversion increases. It is suggested that the formation of aminoethylethanolamine leads to increased piperazine formation at these higher conversions via intramolecular ring closure of AEEA.
U.S. Pat. No. 5,068,329 describes a continuously generated alkyleneamines producers composition rich in AEEA prepared by the reaction of MEA in the presence of a reductive amination catalyst. Ammonia is not used as a reactant. The product distribution shows the production of about 50% to about 90% AEEA, less than about 3% EDA, less than 2% DETA and about 5% to 18% cyclics including PIP, AEP and HEP. The patent lists numerous known reductive amination catalyst useful in the process including those which typically contain metals such as nickel, rhodium, rhenium, zinc, palladium, platinum and the like supported on various materials such as alumina, silica, silica-alumina, kieselguhr, diatomaceous earth and silica-titania.
The patent states that support materials are not equivalent in their ability to form active catalysts and that the actual effectiveness of a material as a support in a potentiated nickel catalyst is generally not predictable in advance. In addition, the nickel-rhenium catalyst disclosed can contain other metals in admixture with the nickel and rhenium which do not detrimentally affect the catalytic properties of the catalyst. It is stated that certain metals can extend the activity life and other physical properties of the Ni--Re catalysts, these metals include lanthanum, calcium, magnesium, strontium, lithium, potassium, barium, cesium, tungsten, iron, ruthenium, copper, silver, zinc, cobalt, uranium, titanium, boron and manganese.
U.S. Pat. No. 5,202,490 describes a process for the manufacture of an alkyleneamines reaction product mixture without a net increase in piperazine by the reaction of MEA and ammonia using a reductive amination catalyst. Again, the product mixture is characterized by the presence of about 15% to 35% DETA, about 10% to about 35% AEEA, about 15% to about 55% EDA (net generated) and about 3% to about 25% cyclics including PIP, AEP and HEP.
The patent describes the same catalysts enumerated above and in addition states that other preferred reduction amination catalysts are composed of rhenium, nickel and boron impregnated on a support material selected from the group consisting of alumina (e.g. alpha), silicas, silica-aluminas, kieselguhrs or diatomaceous earths and silica-titanias, wherein the ratio of nickel to boron to rhenium is in the range of from about 2:2:1 to about 30:30:1 and the total nickel, boron and rhenium present is in the range of about 3 to about 30 percent by weight of the support material.
The increased production of AEEA is achieved by using lower ammonia/MEA mole ratios to favor MEA self condensation. Such changes in reaction conditions may lead to harsher reaction conditions, e.g. higher pH, which may contribute to deactivation and degradation of the catalyst and catalyst supports, and produces larger amounts of undesired aminoalkyl ethanolamines.
It would be beneficial to have a process which increases the selective production of AEEA, without generating large amounts of cyclic alkylenepolyamine products.